This invention relates to antennas which are suitable for transmitting and receiving plane polarised electro-magnetic radiation at a very high frequency, typically in excess of 1 GHz. A dipole is particularly suitable for this purpose, but it has proved difficult to satisfactorily produce an antenna arrangement containing an array of dipoles in which the impedance of the dipole is acceptably constant over a reasonably broad bandwidth. Where a large number of dipoles form part of the antenna arrangement, it is convenient to feed each via a Triplate three-layer transmission line (sometimes termed strip line), if the dipoles lie in the same plane as the Triplate, but the electrical performance can be rather unsatisfactory. The present invention seeks to provide an improved dipole antenna arrangement which utilises a triplate feeder.